The present invention relates to an automation system for an industrial plant, especially a chemical plant the operating parameters of which are subject to supervision and correction by digital electronic calculators with memorized program, as a function of signals proportional to the values of the said operating parameters.
For continuous correct operation of a industrial plant it would be necessary for the operating parameters to remain constant in time at a predetermined value, whereas in the case of non-continuous (batch processing) plants it would be necessary for the operating parameters to be varied in time in accordance with a strict predetermined logic sequence.
It is in fact obvious that any excessive variation in the value of one of the parameters would upset the smooth operation of the system, whereas such variations are unavoidable in practice. Consequently it is important to continually, if not continuously, maintain surveillance on the operating conditions of an industrial plant so as to be able to intervene promptly if the conditions in the plant tend to deviate undesirably from predetermined values, which values may be determined by calculations on the basis of memorized criteria.
In this connection there is at present a tendency to assign the task of supervision and control of industrial plants to checking apparatus including at least one electronic digital computer, this partially or wholly replacing the usual instruments.
The adoption of electronic computers for these purposes has been slowed-down however, because of problems of reliability of such systems. When using conventional instrument supervision and control means, all signals representing the operating parameters of the plant are transmitted to a central control room and processed in parallel, which allows supervision with a very high overall reliability. When digital computers are employed for such purposes the parameters cannot be processed in parallel because, as is known, digital computers are essentially sequential in operation and can only detect in series the signals coming from the plant, and can only intervene serially upon the control members of the said plant.
The use of computers therefore involves the loss of the "parallelism" which is a feature of conventional instrumentation and control techniques with consequent loss of reliability in the system.